Trees do not affect CO2 levels, over long time. The basic reason is explained by why it is also called "carbon cycle". Plants grow, temporarily storing carbon, then die, releasing the carbon back to atmosphere either by burning or by decaying or by being consumed and literally breathed out as CO2 back.
Rather than planting a tree, you can actually help the atmosphere more by cutting a tree and building a house out of it and not letting it rot for a really long time. By cutting the tree and building the house, you are sequestering the carbon for probably longer than the tree would live (depending on what would be its future) and also making space for new trees to grow.
If you are looking to actually affect the long term outcome, you need to do one of two things:
1) stop emitting CO2
2) sequester the atmospheric CO2 somewher, for a really long time.
Rather than planting a tree, you can actually help the atmosphere more by cutting a tree and building a house out of it and not letting it rot for a really long time. By cutting the tree and building the house, you are sequestering the carbon for probably longer than the tree would live (depending on what would be its future) and also making space for new trees to grow.
If you are looking to actually affect the long term outcome, you need to do one of two things:
1) stop emitting CO2
2) sequester the atmospheric CO2 somewher, for a really long time.